Signed Memory Arithmetic vulnerability iOS

Question

I developed a Cordova application and it went through a security review, one of the findings was related to a plugin I use to make curl requests. The finding is graded as Heigh vulnerability. The finding is as follows:

Signed integer sizeof at line 143 of [some file] specifies size of memory to allocate.

#ifdef __LP64__
#define CURL_SIZEOF_LONG 8
#else
#define CURL_SIZEOF_LONG 4
#endif

#define CurlchkszEQ(t, s) sizeof(t) == s ? 1 : -1

typedef char
  __curl_rule_01__
    [CurlchkszEQ(long, CURL_SIZEOF_LONG)];

This is an objective-c code and I am not familiar with it. So my question is what is this vulnerability and how to fix it?